test to reproduce behavior of issue brianc/node-postgres#549
a fix was provided in 5079c1e0c41f431ac2e02c40ebd875d8fbb34004;
test is modeled on query-error-handling-tests.js;
test both kill query and disconnection on prepared statement execution;
make connection error string message consistent between native and non-native;
disable test server-side kill for native as it hangs;
sync can cause error to be emitted so we catch that;
we also move _ending state before _send is called.
capture error message from intermittent failure of copy-tests.js
Merge pull request #572 from letsface/test-prepared-statement-error

test to reproduce behavior of issue brianc/node-postgres#549